1. Field of the Invention
The present invention relates to an image processing apparatus that processes image data such as a visible watermark and an invisible watermark, and to an image forming apparatus and method.
2. Description of the Related Art
In the prior art, with developments in digital technology, a great number of documents have been digitized, and management of such digitized documents has posed an important problem.
In the case of complete digital image data, techniques relating to high-robustness watermarks and retrieval methods are important. However, there is a demand for further techniques in the case of a system, such as a copier, wherein information is handled in a printed medium form and an electronic data form, and a complete digital architecture cannot be adopted.
For instance, the following documents disclose related techniques:
Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2001-203882,
Document 2: Jpn. Pat. Appln. KOKAI Publication No. 2004-7463,
Document 3: Jpn. Pat. Appln. KOKAI Publication No. 2003-228560, and
Document 4: Jpn. Pat. Appln. KOKAI Publication No. 2004-118296.
In the technique disclosed in Document 1, the threshold for error diffusion is cyclically altered, and print data is generated by breaking the cyclically only at a watermark part. Thereby, the watermark is made invisible in ordinary print data. If a cyclic pattern using error diffusion is overlaid on the print data, the watermark image can be made visible.
In the technique disclosed in Document 2, two kinds of watermarks with different anti-attack robustnesses are buried in a copy output. Thus, at the time of input, it is determined whether a document is the original or a copy.
In the technique disclosed in Document 3, different information items are buried in a structured electronic document. Invisible watermark data is buried in an image or the like, and a tag is buried in structured data.
In the technique disclosed in Document 4, an image input/output apparatus and a document management server are made to cooperate to make a search as to whether input image data is present in the document management server. If an original document is present, not input data but data in the document management server is printed out.
In ordinary use of a watermark, a watermark that is invisible is buried to prevent/detect tampering. When a specific requirement is met, the watermark is made visible. In recent years, however, in some uses, a watermark in a visible state is overlaid on an image from the beginning, thereby demonstrating that image data is output from a specific apparatus and preventing tampering. In the case of an invisible watermark, digital management is presupposed. However, in the case of a visible watermark that is directly drawn on an image, even if an original with a visible watermark is copied by an analog copier, it is possible, even thereafter, to specify the apparatus that outputs the original by directly viewing the printed matter.
In the method of Document 1, however, the presence/absence of a watermark is not understandable unless a specific process is executed. In addition, a margin that occupies a major part of a copy document is large, and it is difficult to apply this method to a document that substantially comprises characters. In the method of Document 2, different kinds of watermarks are buried to determine whether the document is a copy or not. However, both watermarks are invisible ones, and it is difficult to apply the watermarks to a document with a large margin.
In the method of Document 3, only one of two kinds of information items can be laid on the print data, and it is difficult to apply this method to a copier. The technique of Document 4 is different from the technique of a watermark, and print data is made to cooperate with document management. An OCR, etc. is used for specifying a document, and it is difficult to specify various kinds of input original documents with high precision.